Mark Peterson, age 11, of Williamsport, Pennsylvania, for his question:

How does the puffer fish inflate himself underwater?

He may gulp enough water to bulge his body like a balloon. Or he may come to the surface and inflate himself with gulps of air. Naturally this amazing fish does not puff himself up with personal pride. He does it from fear, perhaps hoping that inflated size will cause his enemies to pause, at least until he has time to make his escape.

The astonishing puffers belong to the ocean. Most o£ them prefer tropical seas, through some live as far north as Nova Scotia. There are about 90 very different species, all of them able to inflate their bodies to twice their normal sizes. Some grow no longer than five inches and people who specialize in tropical fishes like to have them on display. The average sized puffers are 18 caches long and a giant species measures 36 inches from his tail to his pointed nose. Some are fairly smooth, others have scales like pointed thorns.

All the puffers have sacs below their skin, especially around the tummy region. They also have built in equipment to fill and empty these pockets as they choose. At home below the surface, the handiest filler is water. By swallowing great gulps o£ water, a puffer can double his size in a minute or so. The porcupinefish has thorny scales, normally held flat to his sides. But when he inflates, they stand straight up and he becomes a prickly balloon, maybe a foot or more in diameter. Only his face and tail protrude from the fearsome football andfew enemies come close enough to investigate. The burrfish uses the same tactics on a smaller scale.

If you hoist a puffer from the water, he immediately fills his special pockets with gulps of air. When put back where he belongs, he turns his tummy topside and floats near the surface. When he feels secure enough to return to normal, he exhales the air from his sacs. It takes him several minutes to deflate himself down to his proper size. Then he turns right side up and adjusts to his usual swimming position.

In some parts of the world, puffer meat is eaten, though the organs of some species contain a strong alkaloid called t etrodotoxin. This chemical can be used in medicines. However, if these fish are improperly prepared, it becomes a dangerous and usually fatal poison. The Japanese solve this tricky problem very carefully. A chef may not use puffer meat to cook their fugu dish without very special training. In fact, he must have a fugu license from a qualified fugu school of cookery.

Under normal conditions, the average puffer looks like a rather ordinary fish with an extra large head and high forehead. Often he lives in the rainbow tinted garden of a coral reef. He is a hungry meat eater, usually with strong buck teeth. But he is not noted for courage. When scared, he quickly inflates himself to double his normal size with air or water    and refuses to deflate until the danger departs.